You should try go for Cave key when the event have cave key rebate,it gives you gold essence.

Which give you more survivability.

Golden Rope tools(Injury-decrease critical damage/Deal more Crit dmg to player+Critical-Lesser chance of crit by player/Higher chance of crit-ing player).

Cave key would be one of the best choice from moon coin

Of course if you feel you need to upgrade other power-up system such as Ninja card/Myoboku just go for it.